The wife of celebrity chef Gordon Ramsay has told a judge of her "extremely distressing" discovery that her father and brother were "systematically defrauding" her husband.

Tana Ramsay made the allegation as she gave evidence in a legal action in which her husband is accusing her father, Christopher Hutcheson, of using a ghost writer machine to "forge" his signature.

Mr Ramsay claims the machine was used without his knowledge to make him personally liable for the £640,000-a-year annual rental on the historic York & Albany pub near Regent's Park, London.

He is asking a High Court judge to grant him a declaration the rental guarantee is not binding because his signature "was not lawfully authorised" when the 25-year lease was signed in 2007.

Film director Gary Love, who owns the York & Albany, has described Mr Ramsay's allegation as an "absurd" attempt to wriggle out of his rental commitments.

Mr Hutcheson acted as business manager for the Ramsay group of companies until the chef sacked him and Tana's brother, Adam, on the grounds of "gross misconduct" in 2010.

Tanya married Mr Ramsay in 1996 and has four children with him. Yesterday, the third day of the hearing, she came to the High Court, London, dressed in black and spoke about her "dominating, very clever" father.

Mrs Ramsay, who is a television presenter, writes cookery books and runs a beauty salon, said in her witness statement: "The knowledge that my father and brother had been systematically defrauding my husband was extremely distressing to me."

She said she was aware of the use of the ghost writer machine, which enabled other people to reproduce her husband's signature electronically, but thought it was for signing merchandising when her husband was unavailable. She said: "It did not even occur to me the machine might be used to sign Gordon's signature on anything else."

She recalled "the shock on Gordon's face" and the horror and disbelief when the couple's solicitor told her husband the lease for the York & Albany included a personal guarantee from him for 25 years.

Mrs Ramsay said her husband told her "it takes everything we have ever worked for".

In cross-examination, she told Chancery Division judge Mr Justice Morgan: "Since the departure of my father and my brother from the business it has been a huge upheaval, but certainly I feel very comfortable with what the company has become. Whilst not immediately, it is certainly more transparent and on a much more solid basis."

Agreeing with the suggestion her father was a dominating presence, she said: "Not only for me, but my siblings as well."

He had decided what doctors, dentists and lawyers the family should use and it got to the time when it was "healthier" to break away from him and for herself and her husband to have their own "trusted people", she said.

She added: "My father was someone, in my opinion, very very clever at times at giving enough information to satisfy, but never all.

"I think certainly when Gordon asked questions or sort of wanted to know things, sometimes it would be a case of my father keeping him incredibly busy or out of the country with not enough time to be told everything."

When asked by the judge if her father gave the impression that "Gordon doesn't understand these things and trust me to look after the financial side", Mrs Ramsay replied: "Yes, my lord, that would be true."

Describing the current family rift, Mrs Ramsay said: "I don't really speak to my father since he left the company unless it is concerning his grandchildren - we certainly don't have any comfortable conversations."

Earlier in the case, Mr Ramsay told the judge his "deep and extensive trust" in his father-in-law was entirely misplaced" and Mr Hutcheson had defrauded him and the group "of hundreds of thousands of pounds".

The case continues.